Semiconductor device technology has undergone explosive development in recent years. Many new semiconductor devices have been developed, characteristics of known devices have been vastly improved and device integration has continued to be improved. With regard to device integration, packing densities continue to increase and multifunction integrated devices (e.g., optoelectronic devices such as PINFETs) continue to be developed.
A particularly different problem in semiconductor device technology is precise control of doping profiles in the semiconductor materials. Precise doping profiles improve device characteristics and permit greater packing density for various devices (e.g. memory devices, logic devices, etc.) For example, with field effect transistors, precise confinement of the dopants to the doping region improves such characteristics as cut-off voltage, gain characteristics and transconductance. With semiconductor heterojunction lasers, precise confinement of the doping profile to the barrier layer improves various laser characteristics such as threshold current, power output etc.
A particular problem with obtaining desirable doping profile is the redistribution of dopants occurring during crystal growth. It is highly desirable to limit these redistribution effects so as to be able to control the doping profile obtained in semiconductor devices.
A variety of mechanisms contribute to redistribution effects including diffusion of dopant ions, segregation effects of dopant ions, etc. Segregation effects refer to the movement of dopant ions toward the surface of the semiconductor. Segregation effects are mentioned in a number of publications. In one reference (Crystal Growth of Bulk Crystals: Purification, Doping and Defects by A. J. R. DeKock; Handbook on Semiconductors, Volume 3, S. P. Keller ed, North-Holland, N.Y., 1980, Cha. 4, especially Page 251) segregation effects are used to explain the purification technique known as zone refining. Also, in a paper by A. Y. Cho (Impurity Profiles of GaAs Epitaxial Layers Doped with Sn, Si, and Ge Grown with Molecular Beam Epitaxy, Journal of Applied Physics, Volume 46, No. 4 April 1975), surface segregation effects are used to explain certain doping profiles obtained from crystal structures made by molecular beam epitaxy.
Indeed, segregation effects play a particularly important role with a number of dopant species which would otherwise be used more extensively. For example, tin and zinc have certain very desirable doping characteristics for III-V semiconductor compounds such as gallium arsenide including high specificity to particular doping site. However, segregation effects exhibited by these dopant ions severely limit the use of these dopant ions. Particularly desirable is a procedure which would reduce or eliminate segregation effects and permit fabrication of semiconductor devices with sharp, well defined doping profiles.